This invention relates generally to electronic flash photography. More particularly, it relates to a method and means for improving fill flash photography by synchronizing an electronic flash to a shutter to improve the effective camera sensitivity.
When flash bulbs replaced flash powder, the flash bulbs were fired electrically in synchronization with the camera shutter. As the chemical reaction of the magnesium in the flash bulbs took a period of time, the firing of the flash was initiated before the shutter opened and a slight delay was built into the shutter between the time flash contact on the shutter shorted and the shutter opened. This latency time varied between different bulbs, but was finally standardized as the "M" sync speed. With the advent of electronic flash there was no latency, so a new "X" sync speed was added that waits to fire the flash until the shutter is opened fully. In conventional photography, the shorting of the contact which initiates the flash happens at the leading edge as the shutter first comes fully opened. After the flash fires, the shutter stays open for however long it is set thus continuing to buildup natural light exposure on the film.
There is a problem, however, with the "X" sync, or any short delay period which fires the flash near the beginning of the period when the shutter is opened. For moving objects, as the natural light exposure is much longer than the flash exposure, it continues building after the flash exposure giving streaks in the direction of motion. This effect is opposite from the normal decay process of the eye. As reflected in cartoon drawings, human vision perceives streaks trailing moving objects. To solve this problem, some new cameras, such as the Nikon 8008s in conjunction with the Nikon SB-24 flash, introduced "rear curtain" synchronization. The name comes from two curtains that form a focal plane shutter. Conventional flash photography can be termed "front curtain" synchronization as the flash fires when the front curtain first comes fully open. In "rear curtain" synchronization, the flash fires as the final or rear curtain falls at the end of the exposure interval. Other than multiple flash stroboscopic systems, to the applicant's knowledge, all synchronized flash systems to date fire the flash at either the beginning or the end of an exposure interval.
While the rear curtain synchronization represents an advance in the state of the art of photography, to a great extent we are still in the dark ages of photography. Most amateur photographers cannot take pictures in the natural light of life. Most amateur photographs look cold and stark, as though Thor threw a lightning bolt 3 inches above the camera. For both front and rear curtain flash, almost all pictures are ruined aesthetically by a heavy use of a camera flash, although in dim natural light, the flash often makes the difference between salvaging a record and having no image at all. While too much flash degrades the film image, it is also true that most photographs in dim light are improved with a little flash to fill in the dark shadows. However, mixing flash with natural light will entail leaving the shutter open for a relatively lengthy period of time which for moving objects will cause the blurred images discussed above.
In fill flash photography, the present invention reduces the perceived blurring of the natural light exposure relative to the flash light, thereby either improving the aesthetics of the image by reducing the blurring of the images of moving objects, or allowing a longer exposure time with the same blurring to reach further into dim natural light.